The present invention relates to a coating device for coating traveling webs of material. More particularly, the present invention is directed towards a coating device for coating traveling webs of material, particularly webs of paper, which are guided between a counter-roll and a chamber for feeding coating composition to the web of material. Such a coating device is disclosed in U.S. Pat. No. 3,980,043.
In the coating device disclosed in the foregoing patent, the chamber for receiving the coating composition, usually under pressure, is formed in the shape of an annular space having a slit-like opening facing the web of material to be coated and extending substantially the entire operating width of the counter-roll. Coating material is supplied to the annular space by a feed pipe which extends through the space coaxially therewith. A plurality of outlet openings are formed at spaced locations along the feed pipe on the side of the annular space opposite the slit-like outlet opening of the annular chamber and coating material enters the annular chamber through these openings. As a result of this arrangement, an optimally uniform feeding of coating composition to the web of material is assured, and dead spaces are avoided.
Unfortunately, such feed devices have the disadvantage that air or other gases which are unavoidably present in the coating composition cannot be removed before the application of the composition to the web of material. This leads to stiffness or other undesirable properties of the coating applied to the web of material.
For structural reasons, and to achieve the lightest possible weight, it is desirable in most cases to form the chamber in a triangular rather than an annular shape. The reason for this is as follows. The supporting beam which carries the doctor element (for example a coating blade) is formed, for reasons of strength, as a hollow girder. To minimize the number of structural elements and to reduce the weight of the coating device, the chamber for the coating composition is usually created by providing another wall on the outside of the hollow beam. This results in a chamber which has more of a triangular than an annular outer contour.